Technical data
29.
2.3.1 Air Compressor Panel
Reliable Model B-SI and C-SI Air Compressor Panels provide self-contained supervisory air supply
and pressure maintenance for single interlock preaction systems* with capacity up to 200 gallons. The
Figure 28
MODEL B-SI/C-SI AIR
COMPRESSOR PANEL
air source of the Model B-SI is a 120 VAC, 1/16 HP Gast air
compressor; the Model C-SI is equipped with a 220 VAC,
1/16 HP Gast air compressor. A System Sensor Model
EPS10-2 pressure switch monitors the system air pressure.
Approximately 7 psi (0.48 bar) of air pressure will keep the
pressure switch contacts open and therefore the air com-
pressor motor off. A drop of approximately 2 psi (0.14 bar)
will switch the contact to closed position; the compressor
will turn on to replace the air in the system (in case of a small
leakage). If the pressure continues to drop, at a pressure of
approximately 4 psi (0.28 bar) the low air signal will activate.
An auxiliary relay provides dry contacts for remote signal
of low air pressure and/or loss of power to the building fire
alarm panel or other monitored location. The Model B-SI
and Model C-SI Air Compressor Panels are designed with
keyhole slots for ease of wall mounting. A quick-fill bypass
connection outside the enclosure reduces setup time after
installation, testing, or maintenance.
Refer to Reliable Automatic Sprinkler Company Bulletin 254
for more detailed information on the Model B-SI and C-SI Air
Compressor Panels.
*Note: The Reliable Dry Pilot Line Single Interlock Preaction System may require up to 26 PSI pneu-
matic pressure, therefore, the Model B-SI and C-SI are not to be used with this system. Air compressors
or compressed nitrogen (see below) with appropriate pressure maintenance devices (section 2.4) must
be used.
2.3.2 Air Compressor
NFPA 13 requires that dry systems and double interlock preaction systems be pressurized to normal
operating pressure within 30 minutes (60 minutes for freezers below 5°F). Properly sized dedicated
air compressors or dependable plant air compressors are commonly used for this purpose. Although
not required by NPFA 13 to be listed, consideration should be given to selecting a quality compressor
to avoid maintenance issues and/or false activation of the system. Local electrical codes should also
be consulted to determine if any additional requirements exist (e.g., UL listing). Compressors having
capacities of less than 5.5 CFM at 10 PSI are not required to have an air receiver or air maintenance
device; however, individual maintenance of pressure for each system is required when an automatic air
supply is used to feed multiple systems. This necessitates the use of an air receiver (tank) with a listed
pressure maintenance device on each system.
A tankless compressor without pressure switch or “bare” compressor can be used to supply a single
dry system or single interlock preaction system. Bare compressors require an auxiliary means of motor
control such as the Reliable Model B-1 Pressure Maintenance Device (see 2.4.2.). The factory supplied
pressure switch on the Model B-1 directly monitors system pressure and starts/stops the compressor
motor. System air pressure will fluctuate from high to low via the compressor start/stop controller. An
A-2 Air Maintenance Device will cause compressor to short cycle. Note: The pressure switch on the
Model B-1 Pressure Maintenance Device is not a low pressure supervisory switch. An air receiver (tank)
is not required by NFPA 13 when the compressor has a capacity less than 5.5 CFM at 10 PSI.
Tank-mounted air compressors provide a convenient means of meeting the requirement for an air
receiver when compressor capacity is 5.5 CFM at 10 PSI or greater, or when a tank is otherwise man-
dated. Tank mounted compressors are provided with a pressure switch that monitors the tank pressure
and starts/stops the compressor motor at the desired settings. Air pressure from the tank is regulated
(“bled”) into the system or systems through a listed pressure maintenance device such as the Reliable
Model A-2 (see 2.4.1.). Tank-mounted systems, even when not required, can help prevent short-cycling
and thereby extend the life of air compressors, and can also be helpful in preventing ice build-up in
freezer systems. When supplying multiple systems, the compressor must be selected to pressurize the
largest system within the time frame required by NFPA 13.
Reliable recommends that a tank mounted compressor along with a listed air maintenance device be
used on all systems. This is particularly important with double interlock preaction systems where loss
of pneumatic pressure is used as one of the releasing conditions. Tank mounted compressors also
provide a reserve supply of pressurized air in the event of power outages.